Bridge type coordinate measuring machine

ABSTRACT

A bridge type coordinate measuring machine characterized by a bridge (20) that has a closed loop configuration encircling the measuring machine base (10). The bridge (20) includes two uprights (21, 22), an upper member (23) connecting the uprights together and at least one lower member (24) connecting the uprights together below the upper surface (11) of the base (10). Bearings (41) for the bridge are offset inwardly from the vertical axes of the uprights of the bridge and a guideway (12, 13), along which the bearings travel, is located on each side of the base. The bearings (41) operate upwardly, downwardly and sidewardly against the surfaces of the guideways (12, 13) located on the sides of the base (10). This arrangement both stiffens and raises the resonant frequency of the bridge, thereby improving the measuring accuracy and repeatability of the coordinate measuring machines performance.

This invention relates to a bridge type coordinate measuring machine(CMM) for measuring the dimensions of a workpiece.

A bridge type coordinate measuring machine is generally comprised of abase, a bridge .[.moveably.]. .Iadd.movably .Iaddend.mounted to thebase, a carriage .[.moveably.]. .Iadd.movably .Iaddend.mounted to theupper portion of the bridge, a probe .[.moveably.]. .Iadd.movably.Iaddend.mounted to the carriage and a measuring and computation systemthat responds to movement of the probe for measuring the dimensions of aworkpiece located on the upper surface of the base. Examples of bridgetype coordinate measuring machines may be found in U.S. Pat. Nos.3,749,501 entitled "Measuring Machine" issued July 31, 1973; and3,840,993 entitled "Coordinate Measuring Machine" issued Oct. 15, 1974.The important functions of a coordinate measuring machine are itsaccurate measurement and its repeatability i.e. ability to repeat orobtain the same measurement from the same workpiece. In a bridge typecoordinate measuring machine accuracy and repeatability may be adverselyaffected by vibration and relative movement between the uprights of thebridge. Poor stiffness or ridigity of the bridge permits relativemovement between the uprights of the bridge while height, spacing andstiffness all affect resonant frequency, which if low, makes themeasuring probe mounted on the bridge more susceptible to vibrations.

One approach to minimizing or dampening the effect of vibrations on aCMM has been to mount the CMM on an air bag apparatus or large concreteplatform. These approaches are expensive, space consuming and onlyisolate external vibrations i.e., ground vibrations. Internal vibrationse.g., caused by electro mechanical servo mechanisms mounted on themachine, would not be isolated or dampened.

One approach to minimizing the effect of relative movement between thebridge uprights is discussed in the U.S. Pat. No. 3,749,501 patent wherea position indicator is located on each upright. However, this increasesthe cost for the positional and measurement apparatus of the CMM andstill does not address the problem of an undesirable low resonantfrequency that can be present in a bridge structure e.g. a resonantfrequency below 20 Hertz can adversely effect the measuring accuracy ofa CMM.

Accordingly, the accuracy of the measurements made by a bridge typecoordinate measuring machine may be adversely affected by poor rigidityand vibrations because of a low resonant frequency of the bridge. Thisis especially true of a bridge type CMM used for measuring largeworkpieces, such as an automobile body or engine, because of the heightand spacing of the uprights of such a bridge e.g., about one to twometers high with one and a half to two and a half meter spacing.

DISCLOSURE OF THE INVENTION

The invention is a bridge type coordinate measuring machine that has aclosed loop bridge configuration that encircles the upper surface of ameasuring machine base upon which a workpiece is placed for measurementand is characterized by the location of the bearings for the bridgebeing offset from the vertical axes of the uprights of the bridge and bya guideway for the bearings located on each side of the base.

.Iadd.The invention also is a bridge type coordinate measuring machinecharacterized by a closed loop bridge configuration that encircles theupper surface of the base, and a plurality of bearings positioned totransmit force between the bridge and the base at least vertically andhorizontally.

According to another aspect of the invention, a bridge type coordinatemeasuring machine is provided, characterized by means for movablymounting the bridge to the base which includes at least a first pair oflaterally spaced bearings, and a closed loop configuration whichencircles the upper surface of the base and the first pair of bearings,wherein the closed loop configuration is formed by a second memberconnecting together the uprights of the bridge below the upper surfaceof the base.

According to another aspect of the invention, a bridge type coordinatemeasuring machine is provided, characterized by a closed loop bridgeconfiguration encircling the upper surface of the base, and means formovably mounting the bridge to the base which includes first, second andthird pairs of bearings positioned to transmit force between the bridgeand the base, wherein the first pair of bearings operate in a verticaldirection, the second pair of bearings operate in a horizontal directionand in opposition to each other, and the third pair of bearings operatein vertical directions respectively opposite those of the first pair ofbearings.

A further aspect of the invention resides in a bridge type coordinatemeasuring machine, characterized by a closed loop bridge configurationwhich encircles the upper surface of the base in which the closed loopconfiguration is formed by means for connecting together the uprights ofthe bridge below the upper surface of the base, and means for movablymounting the bridge to the base which includes first and second pairs ofbearings, wherein the first pair of bearings has a first bearingcoacting with the base, and one of the uprights and a second bearingcoacting with the base and the other upright, and wherein the secondpair of bearings is located between the uprights below at least aportion of the means for connecting together the uprights and operatingin a horizontal direction.

A still further aspect of the invention resides in a bridge typecoordinate measuring machine, characterized by a closed loop bridgeconfiguration that encircles the upper surface of the base, and meansfor movably mounting the bridge to the base which includes a first pairof bearings applying forces in opposite directions to each other in avertical plane, a second pair of bearings applying forces in oppositedirections to each other in a horizontal plane, and a third pair ofbearings applying forces in opposite direction to each other in avertical plane spaced from the vertical plane of the first pair ofbearings, and wherein all of the bearings are positioned to transmitforces between the bridge and the base.

The invention also consists of a bridge type coordinate measuringmachine, characterized by a closed loop bridge configuration encirclingthe upper surface of the base and at least a portion of means formovably mounting the bridge to the base, wherein the closed loopconfiguration is formed by a second member connecting together theuprights of the bridge.

A further aspect of the invention resides in a bridge type coordinatemeasuring machine, characterized by a closed loop bridge configurationdefined by a first loop encircling the upper surface of the base, and asecond loop below the first loop.

According to another aspect of the invention, a bridge type coordinatemeasuring machine is provided, characterized by a closed loop bridgeconfiguration encircling the upper surface of the base, wherein theclosed loop configuration is formed by a second member connectingtogether the uprights of the bridge at the lower ends of the uprights.

According to a still further aspect of the present invention, a bridgetype coordinate measuring machine is characterized by a bridge having aclosed loop configuration encircling the upper surface of the base inwhich the closed loop configuration is formed by a second memberconnecting together the uprights at a position below the upper surfaceof the base, and the bridge is mounted on the base by means of a pair oflaterally spaced bearing means, each of the bearing means acting in atleast vertical and horizontal directions, the pair of bearing meansbeing arranged such that the forces transmitted by the pair of bearingmeans are symmetrically balanced with respect to the center of thebridge. .Iaddend.

One advantage of this invention is that it improves the measuringaccuracy of a CMM used for measuring large workpieces such as anautomobile engine or body.

Another advantage of this invention is that it improves the ridigity ofthe bridge of a CMM.

Another advantage of this invention is that it lowers the effect ofvibrations on the probe mounted on the bridge of a CMM by increasing theresonant frequency of the bridge.

Another advantage of this invention is that it minimizes the need for anexpensive system to isolate the measuring probe of a CMM from externalvibrations.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 are perspective views of a bridge type coordinatemeasuring machine incorporating the principles of this invention.

FIG. 3 is a cutaway view of a CMM showing one arrangement of the bridgemounted to the base of a CMM.

FIG. 4 is still another arrangement of a bridge mounted to the base of aCMM.

Referring now to the drawings, FIG. 1 illustrates a bridge typecoordinate measuring machine of the type having a base 10, a bridge 20.[.moveably.]. .Iadd.movably .Iaddend.mounted to the base 10, a carriage50 .[.moveably.]. .Iadd.movably .Iaddend.mounted to the bridge 20, and aprobe 30 .[.moveably.]. .Iadd.movably .Iaddend.mounted to the carriage50. The base 10 includes an upper surface 11 upon which a workpiece (notshown) to be measured is located and guideways 12, 13. The base 10 isdivided into an upper table portion 14 separated from the lower portionby legs 15. Rubber feet 16 at the bottom of the base 10, minimize theaffect of external vibrations on the CMM. This arrangement of the guideways 12, 13, and legs 15 provides space, if desired, for a motor andsuitable drive mechanism for moving the bridge 20 to be located at thecenter of the base 10. The bridge 20 includes two uprights 21, 22connected together by an upper member 23 and a lower member 24. Moveablymounted on the upper member 23 of the bridge 20 is a carriage 50 whichhas .[.moveably.]. .Iadd.movably .Iaddend.mounted thereto a probe shaft31 having a probe 30 at one end thereof. The probe 30 is generally ofthe type that, upon contact with a piece to be measured, provides asignal to appropriate computation and measuring apparatus. One exampleof such a probe may be found in U.S. Pat. No. 4,270,275 entitled"Probes" and issued June 6, 1981. The bridge 20 is .[.moveably.]..Iadd.movably .Iaddend.mounted to the base 10 along guide ways 12, 13,the surfaces of which interface with bearings 41 mounted in respectivechannels 25 in the bridge 20. Preferably, air bearings 41 are used tofacilitate movement of the bridge 20 along the guideways 12, 13 of thebase 10. Movement of the bridge, carriage and probe shaft 31 allows theprobe to move and take measurements in three dimensions. Electrical ormechanical means responsive to movement of the probe indicate theposition of the probe in 3 coordinates and, when required, calculatemeasurements e.g., The Warner and Swasey Company, Sheffield MeasurementDivision measurement processor model MP3.

FIG. 2 illustrates how the carriage 50 is .[.moveably.]. .Iadd.movably.Iaddend.mounted to the upper member 23 of the bridge 20 along guideways26, 27, 28 the surfaces of which interface with bearings 55 inrespective channels 51, 52, 53 in the carriage 50. The probe 30 ismounted to the bridge 20 for movement along 2 .[.axis.]. .Iadd.axes.Iaddend.and is moveable along a third axis by movement of the bridge.Mounting arrangements for the probe and carriage are described infurther detail in the U.S. Pat. Nos. 3,749,501 and 3,840,993. Mechanicalor preferably air bearings 55 are used to facilitate movement of thecarriage 50 relative to the bridge 20. Also shown is the arrangement ofthe upper and lower bearings 41 of the bridge 20 that coact with thesurfaces of one of the guide ways 12 of the base 10.

FIG. 3 illustrates further details of how the air bearings 41, located.Iadd.essentially U-shaped .Iaddend.in channels 25 in the bridge 20,interface with the surfaces of the guide ways 12, 13 of the base 10..Iadd.The air bearings 41 include first and second laterally spacedpairs thereof. The first laterally spaced pair of bearings 41 bearvertically upward from the guideways 12, 13 respectively againsthorizontal surfaces carried by the uprights 21, 22 and which form partof the channels 25. The second laterally spaced pair of the bearings 41bear vertically downward against the lower member 24, such that thefirst and second pairs of bearings act in opposite vertical directions.Further, the air bearings 41 include a third pair thereof whichrespectively bear horizontally from the guideways 12, 13 against theuprights 21, 22 and in opposite horizontal directions, perpendicular tothe vertical direction in which the first and second pairs of airbearings act. As a result of the bearing arrangement described above,the forces transmitted by the bearings 41 on each side of the bridge 20are symmetrically balanced with respect to the center of the bridge 20..Iaddend.Preferably, the lower member 24 of the bridge 20 is locatedabove the bearings 41 and below the table portion 14 of the base 10. Theupper table portion 14 of the base 10 is supported by only three legs15. This provides better vibrational and deflectional isolation thanwould four legs i.e., one in each corner of the table 14.

FIG. 4 illustrates an alternate embodiment of the invention wherein thebridge 20 has two lower connecting members 24, 29 with the bearings 41coacting with the guide ways 12, 13 of the base 10 located between the 2lower members 24, 29 of the bridge 20.

I claim:
 1. A bridge type coordinate measuring machine of the typehaving a base (10) having an upper surface (11) for supporting a workpiece to be measured, a bridge (20) having two uprights (21, 22) and afirst member (23) connecting the uprights (21, 22) together above theupper surface (11) of said base (10), means (12, 13, 41) for.[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) to thebase (10), a probe (30), and means (50, 31) for mounting said probe (30)to the first member (23) of said bridge (20) for movement relative tosaid bridge and to said base (10), characterized in that:the bridge (20)has a closed configuration that encircles the upper surface (11) of saidbase (10) said closed loop configuration formed by a second member (24)connecting together the uprights (21, 22) of the bridge (20) below theupper surface (11) of said base (10) and below the means (12, 13) for.[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) to thebase (10).
 2. A bridge type coordinate measuring machine of the typehaving a base (10) having an upper surface (11) for supporting a workpiece to be measured, a bridge (20) having two uprights (21, 22) and afirst member (23) connecting the uprights (21, 22) together above theupper surface (11) of said base (10), means (12, 13, 41) for.[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) to thebase (10), a probe (30), and means (50, 31) for mounting said probe (30)to the first member (23) of said bridge (20) for movement relative tosaid bridge and to said base (10), characterized in that:the bridge (20)has a closed loop configuration that encircles the upper surface (11) ofsaid base (10) said closed loop configuration formed by a second member(24) connecting together the uprights (21, 22) of the bridge (20) belowthe upper surface (11) of said base (10); and by the means for.[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) to thebase (10) includes a pair of guideways (12, 13), one of said guideways(12) located on one side of said base (10) and the other of saidguideways (13) located on the opposite side of said base (10), saidguideways (12, 13) coacting with bearings (41) in a respective channel(25) in each of said uprights (21, 22) of said bridge (20) to facilitatemovement of said bridge (20) on said base, said second member (24)connecting the uprights (21, 22) of the bridge (20) together locatedbelow said guideways (12, 13).
 3. A bridge type coordinate measuringmachine of the type having a base (10) having an upper surface (11) forsupporting a work piece to be measured, a bridge (20) having twouprights (21, 22) and a first member (23) connecting the uprights (21,22) together above the upper surface (11) of said base (10), means (12,13, 41) for .[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge(20) to the base (10), a probe (30), and means (50, 31) for mountingsaid probe (30) to the first member (23) of said bride (20) for movementrelative to said bridge and to said base (10), characterized in that:thebridge (20) has a closed loop configuration that encircles the uppersurface (11) of said base (10) said closed loop configuration formed bya second member (24) connecting together the uprights (21, 22) of thebridge (20) below the upper surface (11) of said base (10); and byguideways (12, 13) along which said bridge (20) is .[.moveable.]..Iadd.movable .Iaddend.and a third member (29) connecting the uprights(21, 22) of the bridge (20) together below the surface (11) of said base(10) and above said guideways (12, 13), said second member (24)connecting together the uprights (21, 22) of the bridge (20) locatedbelow said guideways (12, 13).
 4. A bridge type coordinate measuringmachine as described in claim 3 wherein the height of each of the twouprights (21, 22) is greater than one meter.
 5. A bridge type coordinatemeasuring machine of the type having a base (10) having an upper surface(11) for supporting a work piece to be measured, a bridge (20) having aclosed loop configuration that encircles the upper surface (11) of saidbase (10) said closed loop configuration formed by two uprights (21,22), a first member (23) connecting the uprights (21, 22) together abovethe upper surface (11) of said base (10), and a second member (24)connecting together the uprights (21, 22) of the bridge (20) below theupper surface (11) of said base (10), means (12, 13, 41) for.[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) to thebase (10), a probe (30), and means (50, 31) for mounting said probe (30)to the first member (23) of said bridge (20) for movement relative tosaid bridge and to said base (10), the means for .[.moveably.]..Iadd.movably .Iaddend.mounting the bridge (20) to the base (10)characterized by:a pair of guideways (12, 13), located below the uppersurface (11) of the base (10), one of said guideways (12) located on oneside of said base (10) and the other of said guideways (13) located onthe opposite side of said base (10), each of said guideways (12, 13)coacting with respective bearings (41) located in a respective channel(25) formed between said second member (24), and an inwardly extendingportion of each of said uprights (21, 22).
 6. A coordinate measuringmachine as described in claim 5 wherein said bearings (41) includebearings that coact against upwardly and downwardly facing surfaces of arespective guideway (12, 13).
 7. A coordinate measuring machine asdescribed in claim 6 wherein said bearings (41) include bearings thatcoact against a side of each of the guideways (12, 13).
 8. A coordinatemeasuring machine as described in claim 6 including a third member (29)connecting the uprights (21, 22) of the bridge (20) together below thesurface (11) of said base (10) and above said guideways (12, 13).
 9. Abridge type coordinate measuring machine as described in claim 5,wherein the bearings (41) are located between the vertical axes of theuprights (21, 22).
 10. A bridge type coordinate measuring machine asdescribed in claim 6 wherein the bearings (41) are located between thevertical axes of the uprights (21, 22).
 11. A bridge type coordinatemeasuring machine as described in claim 7 wherein the bearings (41) arelocated between the vertical axes of the uprights (21, 22).
 12. A bridgetype coordinate measuring machine as described in claim 6 wherein thebearings (41) coacting upwardly and downwardly are located beneath theupper surface (11) of the base (10).
 13. A bridge type coordinatemeasuring machine as described in claim 7 wherein the bearings (41)coacting upwardly and downwardly are located beneath the upper surface(11) of the base (10).
 14. A bridge type coordinate measuring machine asdescribed in claim 8 wherein the bearings (41) coacting upwardly anddownwardly are located beneath the upper surface (11) of the base (10).15. A bridge type coordinate measuring machine as described in claim 10wherein the bearings (41) coacting upwardly and downwardly are locatedbeneath the upper surface (11) of the base (10).
 16. A bridge typecoordinate measuring machine as described in claim 11 wherein thebearings (41) coacting upwardly and downwardly are located beneath theupper surface (11) of the base (10).
 17. A bridge type coordinatemeasuring machine as described in claim 5 wherein the second member (24)is located below the bearings.
 18. A bridge type coordinate measuringmachine as described in claim 17 including a third member (29)connecting the uprights (21, 22) of the bridge together below thesurface (11) of the base (10) and above the guideways (12, 13).
 19. Abridge type coordinate measuring machine of the type having a base (10)having an upper surface (11) for supporting a work piece to be measured,a bridge (20) having a closed loop configuration that encircles theupper surface (11) of said base (10) said closed loop configurationformed by two uprights (21, 22), a first member (23) connecting theuprights (21, 22) together above the upper surface (11) of said base(10), and a second member (24) connecting together the uprights (21, 22)of the bridge (20) below the upper surface (11) of said base (10), means(12, 13, 41) for .[.moveably.]. .Iadd.movably .Iaddend.mounting thebridge (20) to the base (10), a probe (30), and means (50, 31) formounting said probe (30) to the first member (23) of said bridge (20)for movement relative to said bridge and to said base (10), the meansfor .[.moveably.]. .Iadd.movably .Iaddend.mounting the bridge (20) tothe base (10) characterized by:a pair of guideways (12, 13), each ofsaid guideways (12, 13) coacting with a respective plurality of bearings(41), said guideways and bearings located directly below the uppersurface (11) of the base (10), one of said guideways (12) and itsrespective bearings (41) located at one side of said base (10) and theother of said guideways (13) and its respective bearings (41) located atthe opposite side of said base (10).
 20. A coordinate measuring machineas described in claim 19 wherein said bearings (41) coact againstupwardly and downwardly facing surfaces of a respective guideway (12,13).
 21. A coordinate measuring machine as described in claim 20 whereinsaid bearings (41) also coact against a side of each of the guideways(12, 13).
 22. A coordinate measuring machine as described in claim 19wherein said bearings (41) are located between the vertical axes of theuprights (21, 22). .Iadd.
 23. In combination, a bridge type coordinatemeasuring machine of the type having a base (10) having an upper surface(11) for supporting a workpiece to be measured, a bridge (20) having twouprights (21, 22) and a first member (23) connecting said uprights (21,22) together above the upper surface (11) of said base (10) , means (12,13, 41) for movably mounting said bridge (2) to said base (10) , a probe(30) , and means (50, 31) for mounting said probe (30) to a first member(23) of said bridge (20) for movement relative to said bridge and tosaid base (10) , characterized in that:the bridge (20) has a closed loopconfiguration that encircles the upper surface (11) of said base (10) ,said closed loop configuration being formed by a second member (24)connecting together the uprights (21, 22) of the bridge (20) below theupper surface (11) of said base (10) and below the means (12, 13) formovably mounting the bridge (20) to the base (10) , and the means (12,13, 14) for movably mounting the bridge to the base (10) includes aplurality of bearings (41) positioned to transmit force between saidbridge (2) and said base (10) at least vertically and horizontally..Iaddend. .Iadd.
 24. A coordinate measuring machine as described inclaim 23, wherein said bearings (41) include air bearings. .Iaddend..Iadd.25. A coordinate measuring machine as described in claim 23,wherein said bearings (41) include at least a first pair of laterallyspaced bearings respectively acting in a vertical direction against apair of surfaces of said bridge (20). .Iaddend. .Iadd.26. A coordinatemeasuring machine as described in claim 25, wherein said pair ofsurfaces of said bridge (20) against which said spaced bearingsrespectively act are respectively defined within a pair of channels (25)in said bridge (20). .Iaddend. .Iadd.27. A coordinate measuring machineas described in claim 26, wherein each of said channels (25) isessentially U-shaped. .Iaddend. .Iadd.28. A coordinate measuring machineas described in claim 27, wherein said channels open inwardly towardeach other. .Iaddend. .Iadd.29. A coordinate measuring machine asdescribed in claim 26, wherein a portion of each of said channels (25)is defined by said second member (24). .Iaddend. .Iadd.30. A coordinatemeasuring machine as described in claim 28, wherein a portion of each ofsaid channels (25) is defined by said second member (24). .Iaddend..Iadd.31. A coordinate measuring machine as described in claim 25,wherein said first pair of bearings are air bearings. .Iaddend..Iadd.32. A coordinate measuring machine as described in claim 26,wherein said pair of bearings and said surfaces are disposed within saidclosed loop so as to be surrounded by said bridge (20). .Iaddend..Iadd.33. A coordinate measuring machine as described in claim 32,wherein said pair of bearings are air bearings. .Iaddend. .Iadd.34. Acoordinate measuring machine as described in claim 25, wherein said pairof bearings is wholly disposed above said second member (24). .Iaddend..Iadd.35. A coordinate measuring machine as described in claim 23,wherein:said bearings (41) includes at least a first pair of laterallyspaced bearings respectively acting in a vertical direction against apair of surfaces of said bridge (20), said pair of bearings and saidsurfaces are disposed within said closed loop so as to be surrounded bysaid bridge (20) , and the entirety of said second member (24) is spacedbelow said pair of bearings. .Iaddend. .Iadd.36. A coordinate measuringmachine as described in claim 35, wherein said bridge (20) includes apair of laterally spaced channels (25) opening toward each other, andsaid pair of surfaces are respectively defined within said channels(25). .Iadd.37. A coordinate measuring machine as described in claim 36,wherein said pair of surfaces extend parallel to said second member(24). .Iaddend. .Iadd.38. A coordinate measuring machine as described inclaim 25, wherein said bearings (41) include a second pair of laterallyspaced bearings respectively acting in a vertical direction against apair of surfaces carried by said base (10), said first and second pairsof bearings acting to transmit force in opposite directions respectivelyupwardly and downwardly. .Iaddend. .Iadd.39. A coordinate measuringmachine as described in claim 38, wherein said bearings (41) include athird pair of laterally spaced bearings acting in a horizontaldirection. .Iaddend. .Iadd.40. A coordinate measuring machine asdescribed in claim 23, wherein said bearings (41) include first andsecond sets of bearings respectively acting in two directionsperpendicular to each other. .Iaddend. .Iadd.41. In combination, abridge type coordinate measuring machine of the type having a base (10)having an upper surface (11) for supporting a workpiece to be measured,a bridge (20) having two uprights (21, 22) and a first member (23)connecting said uprights (21, 22) together above the upper surface (11)of said base (10), means (12, 13, 41) for movably mounting said bridge(20) to said base (10), a probe (30), and means for mounting said probe(30) on said bridge (20) for movement relative to said bridge and tosaid base (10), characterized in that:said means (12, 13, 41) formovably mounting said bridge to said base (10) includes at least a firstpair of laterally spaced bearings (41); and said bridge has a closedloop configuration that encircles the upper surface (11) of said base(10) and said first pair of bearings, said closed loop configurationbeing formed by a second member (24) connecting together said uprights(21, 22) of the bridge (20) below the upper surface (11) of said base(10). .Iaddend. .Iadd.42. A coordinate measuring machine as described inclaim 41, wherein said first pair of bearings transmit force vertically..Iaddend. .Iadd.43. A coordinate measuring machine as described in claim42, wherein each of said uprights (21, 22) carries a horizontal surfacedisposed within said closed loop, and said pair of bearings respectivelybear against said horizontal surfaces of said uprights (21, 22)..Iaddend. .Iadd.44. A coordinate measuring machine as described in claim43, wherein each of said bearings is an air bearing. .Iaddend. .Iadd.45.A coordinate measuring machine as described in claim 41, wherein saidbridge (20) includes a pair of channels (25) therein, said channels (25)opening toward each other within said closed loop, and said pair ofbearings are respectively disposed within said channels (25). .Iaddend..Iadd.46. A coordinate measuring machine as described in claim 45,wherein each of said channels (25) includes a horizontal surface againstwhich a corresponding one of said bearings bears. .Iaddend. .Iadd.
 7. Acoordinate measuring machine as described in claim 41, wherein:a bridge(2) includes first and second vertically spaced pairs of horizontalsurfaces, said means (12, 13, 41) for movably mounting said bridge (20)to said base (10) includes a second pair of bearings, said first pair ofbearings respectively bear upwardly against said first pair ofhorizontal surfaces, and said second pair of bearings respectively beardownwardly against said second pair of horizontal surfaces. .Iaddend..Iadd.48. A coordinate measuring machine as described in claim 47,wherein said closed loop configuration encircles said second pair ofbearings. .Iaddend. .Iadd.49. A coordinate measuring machine asdescribed in claim 47, wherein said means (12, 13, 41) for movablymounting said bridge (20) to said base (10) includes a third pair ofbearings acting in opposite horizontal directions, and said third pairof bearings is vertically spaced below said first pair of bearings..Iaddend. .Iadd.50. A coordinate measuring machine as described in claim49, wherein said third pair of bearings is vertically positioned betweensaid first and second pair of bearings. .Iaddend. .Iadd.51. A coordinatemeasuring machine as described in claim 47, wherein the bearings in saidfirst pair thereof are respectively spaced inwardly toward each otherfrom the corresponding axes of said uprights (21, 22). .Iaddend..Iadd.52. In combination, a bridge type coordinate measuring machine ofthe type having a base (10) having an upper surface (11) for supportinga workpiece to be measured, a bridge (20) having two uprights (21, 22)and a first member (23) connecting said uprights (21, 22) together abovethe upper surface (11) of said base (10), means (12, 13, 41) for movablymounting said bridge (20) to said base (10), a probe (30), and means(50, 31) for mounting said probe (30) to a first member (23) of saidbridge (20) for movement relative to said bridge and to said base (10),characterized in that:the bridge (20) has a closed loop configurationthat encircles the upper (11) of said base (10), said closed loopconfiguration being formed by a second member (24) connecting togetherthe uprights (21, 22) of the bridge (20) below the upper surface (11) ofsaid base (10) and below the means (12, 13) for movably mounting thebridge (20) to the base (10); and the means (12, 13, 41) for movablymounting the bridge the base (10) includes a first, second and thirdpairs of bearings positioned to transmit force between said bridge (20)and said base (10), said first pair operating in a vertical direction,said second pair operating in a horizontal direction, said bearings insaid second pair operating in opposing directions, and said third pairof bearings operating in a vertical direction opposite the direction ofa respective bearing of said first pair of bearings. .Iaddend. .Iadd.53.A coordinate measuring machine as described in claim 52, wherein saidfirst, second and third pairs of bearings are air bearings. .Iaddend..Iadd.54. A coordinate measuring machine as described in claim 52,wherein said bearings are air bearings. .Iaddend. .Iadd.55. A coordinatemeasuring machine as described in claim 52, wherein said closed loopconfiguration encircles said first pair of bearings. .Iaddend. .Iadd.56.A coordinate measuring machine as described in claim 54, wherein saidclosed loop configuration encircles said first pair of bearings..Iaddend. .Iadd.57. In combination, a bridge type coordinate measuringmachine of the type having a base (10) having an upper surface (11) forsupporting a workpiece to be measured, a bridge (20) having two uprights(21, 22) and a first member (23) connecting said uprights (21, 22)together above the upper surface (11) of said base (10), means (12, 13,41) for movably mounting said bridge (20) to said base (10), a probe(30), and means (50, 31) for mounting said probe (30) to a first member(23) of said workpiece (20) for movement relative to said workpiece andto said base (10), characterized in that:the bridge (20) has a closedloop configuration that encircles the upper surface (11) of said base(10), said closed loop configuration being formed by means (29) forconnecting together the uprights (21, 22) of the bridge (20) below theupper surface (11) of said base (10), said uprights (21, 22)respectively carrying horizontal surfaces; and the means (12, 13, 41)for movably mounting the bridge to the base (10) includes a first andsecond pair of bearings, said first pair having a first bearingvertically coacting with the base and the horizontal surface of oneupright (21) and a second bearing vertically coacting with the base andthe horizontal surface of the other upright (22), said second pair ofbearings located between the uprights below at least a portion of themeans (29) for connecting together the uprights (21, 22) and operatingin a horizontal direction. .Iaddend. .Iadd.58. A coordinate measuringmachine as described in claim 57, wherein said first and second pairs ofbearings are air bearings. .Iaddend. .Iadd.59. A coordinate measuringmachine as described in claim 57, wherein said first and second pairs ofbearings are air bearings. .Iaddend. .Iadd.60. A coordinate measuringmachine as described in claim 57, wherein said connecting means includesat least a first connecting member (24), and said closed loopconfiguration encircles said first pair of bearings. .Iaddend. .Iadd.61.A coordinate measuring machine as described in claim 60, wherein saidconnecting means includes a second connecting member (29) verticallyspaced from said first connecting member (24), and wherein said secondpair of bearings is positioned between said first connecting member (24)and said second connecting member (29). .Iaddend. .Iadd.62. A coordinatemeasuring machine as described in claim 60, wherein said first andsecond pairs of bearings are air bearings. .Iaddend. .Iadd.63. A bridgetype coordinate measuring machine according to claim 57 including athird pair of bearings coacting with the base and the bridge (20), saidthird pair of bearings operating in a direction perpendicular to thedirection of operation of said second pair of bearings and in adirection opposite said first pair of bearings. .Iaddend. .Iadd.64. Acoordinate measuring machine as described in claim 61, wherein saidfirst and second pairs of bearings are air bearings. .Iaddend. .Iadd.65.A coordinate measuring machine as described in claim 63, wherein saidthird pair of bearings are air bearings. .Iaddend. .Iadd.66. Acoordinate measuring machine as described in claim 60, including a thirdpair of bearings coacting with the base and the bridge (20), said thirdpair of bearings operating in a direction perpendicular to the directionof operation of said second pair of bearings and in a direction oppositesaid first pair of bearings. .Iaddend. .Iadd.67. In combination, abridge type coordinate measuring machine of the type having a base (10)having an upper surface (11) for supporting a workpiece to be measured,a bridge (20) having two uprights (21, 22) and a first member (23)connecting said uprights (21, 22) together above the upper surface (11)of said base (10), means (12, 13, 41) for movably mounting said bridge(20) to said base (10), a probe (30), and means (50, 31) for mountingsaid probe (30) to a first member (23) of said workpiece (20) formovement relative to said bridge and to said base (10), characterized inthat:the bridge (20) has a closed loop configuration that encircles theupper surface (11) of said base (10), said closed loop configurationbeing formed by a second member (24) connecting together the uprights(21, 22) of the bridge (20) below the upper surface (11) of said base(10) and below the means (12, 13) for movably mounting the bridge (20)to the base (10); and the means (12, 13, 41) for movably mounting thebridge (20) to the base (10) includes a first pair of bearings applyingforces in opposite directions to each other in a vertical plane, asecond pair of bearings applying forces in opposite directions to eachother in a horizontal plane, a third pair of bearings applying forces inopposite directions to each other in a vertical plane spaced from thevertical plane of said first pair of bearings, all of said bearingspositioned to transmit forces between said bridge (20) and said base(10). .Iaddend. .Iadd.68. A coordinate measuring machine as described inclaim 67, wherein said first, second and third pair of bearings are airbearings. .Iaddend. .Iadd.69. A coordinate measuring machine asdescribed in claim 67, wherein all of said first, second and thirdbearings are air bearings. .Iaddend. .Iadd.70. A coordinate measuringmachine as described in claim 67, wherein said closed loop configurationencircles said first pair of bearings. .Iaddend. .Iadd.71. A coordinatemeasuring machine as described in claim 68, wherein said closed loopconfiguration encircles said first pair of bearings, and said first pairof bearings are air bearings. .Iaddend. .Iadd.72. In combination, abridge type coordinate measuring machine of the type having a base (10)having an upper surface (11) for supporting a workpiece to be measured,a bridge (20) having two uprights (21, 22) and a first member (23)connecting said uprights (21, 22) together above the upper surface ofsaid base (10), means (12, 13, 41) for movably mounting said bridge (20)to said base (10), a probe (30), and means (50, 31) for mounting saidprobe (30) to said first member (23) of said bridge (20) for movementrelative to said bridge (20) and to said base (10), characterized inthat:the bridge (20) has a closed loop configuration encircling theupper surface (11) of said base (10) and at least a portion of the means(12, 13, 41) for movably mounting said bridge (20) to said base (10),said closed loop configuration being formed by a second member (24)connecting together the uprights (21, 22) of the bridge (20). .Iaddend..Iadd.73. A bridge type coordinate measuring machine as described inclaim 72, wherein said mounting means (12, 13, 41) includes first andsecond bearings each transmitting force in a vertical direction andsecond end and third bearings each transmitting force in a horizontaldirection. .Iaddend. .Iadd.74. A bridge type coordinate measuringmachine as described in claim 73, wherein said portion of said mountingmeans (12, 13, 41) includes said first and second bearings. .Iaddend..Iadd.75. A bridge type coordinate measuring machine as described inclaim 74, wherein said first and second bearings are laterally spacedapart. .Iaddend. .Iadd.76. In combination, a bridge type coordinatemeasuring machine of the type having a base (10) having an upper surface(11) for supporting a workpiece to be measured, a bridge (20) having twouprights (21, 22) and a first member (23) connecting said uprights (21,22) together above the upper surface of said base (10), means (12, 13,41) for movably mounting said bridge (20 ) to said base (10), a probe(30), and means (50, 31) for mounting said probe (30) to said firstmember (23) of said bridge (20) for movement relative to said bridge(20) and to said base (10), characterized in that:the bridge (20) has aclosed loop configuration defined by a first loop encircling the uppersurface (11) of said base (10) and a second loop below said first loop..Iaddend. .Iadd.77. A bridge type coordinate measuring machine asdescribed in claim 76, wherein at least a portion of said mounting meansis encircled by said second loop. .Iaddend. .Iadd.78. A bridge typecoordinate measuring machine as described in claim 77, wherein saidportion of said mounting means includes first and second bearingstransmitting force in a horizontal direction. .Iaddend. .Iadd.79. Abridge type coordinate measuring machine as described in claim 78,wherein said first and second bearings are respectively inboard of saiduprights (21, 22). .Iaddend. .Iadd.80. A bridge type coordinatemeasuring machine as described in claim 76, wherein said first loop isformed by a second member (29) connecting together said uprights (21,22) of the bridge (20) below the upper surface (11) of said base (10)..Iaddend. .Iadd.81. A bridge type coordinate measuring machine asdescribed in claim 80, wherein said second loop is formed by said secondmember (29) and a third member (24) below said second member (29)..Iaddend. .Iadd.82. A bridge type coordinate measuring machine asdescribed in claim 81, wherein said mounting means (12, 13, 41) includesfirst and second bearings disposed between said first and second members(29, 24) and each transmitting force in a horizontal direction..Iaddend. .Iadd.83. In combination, a bridge type coordinate measuringmachine of the type having a base (10) having an upper surface (11) forsupporting a workpiece to be measured, a bridge (20) having two uprights(21, 22) and a first member (23) connecting said uprights (21, 22)together above the upper surface of said base (10), means (12, 13, 41)for movably mounting said bridge (20) to said base (10), a probe (30),and means (50, 31) for mounting said probe (30) to said first member(23) of said bridge (20) for movement relative to said bridge (20) andto said base (10), characterized in that:the bridge (20) has a closedloop configuration encircling the upper surface (11) of said base (10),said closed loop configuration being formed by a second member (24)connecting together the uprights (21, 22) of the bridge (20) at thelower ends of said uprights (21, 22). .Iaddend. .Iadd.84. A bridge typecoordinate measuring machine as described in claim 83, wherein at leasta portion of said mounting means (12, 13, 41) includes bearings (41)disposed inboard of said uprights (21, 22). .Iaddend. .Iadd.85. Incombination, a bridge type coordinate measuring machine of the typehaving a base (10) having an upper surface (11) for supporting aworkpiece to be measured, a bridge (20) having two uprights (21, 22) anda first member (23) connecting said uprights (21, 22) together above theupper surface of said base (10), means (12, 13, 41) for movably mountingsaid bridge (20) to said base (10), a probe (30), and means (50, 31) formounting said probe (30) to said first member (23) of said bridge (20)for movement relative to said bridge (20) and to said base (10),characterized in that:the bridge (20) has a closed loop configurationencircling the upper surface (11) of said base (10), said closed loopconfiguration being formed by a second member (24) connecting togetherthe uprights (21, 22) at a position below the upper surface (11) of saidbase (10), and the mounting means (12, 13, 41) includes a pair oflaterally spaced bearing means, each of the bearing means acting in atleast vertical and horizontal directions, said pair of bearing meansbeing arranged such that the forces transmitted by said pair of bearingmeans are symmetrically balanced with respect to the center of thebridge (20). .Iaddend. .Iadd. A bridge type coordinate measuring machineas described in claim 85, wherein each of said bearing means includes abearing acting vertically upward, and a bearing acting horizontally..Iaddend. .Iadd.87. A bridge type coordinate measuring machine asdescribed in claim 86, wherein said horizontally acting bearing actsoutwardly. .Iaddend. .Iadd.88. A bridge type coordinate measuringmachine as described in claim 86, wherein each of said bearing meansincludes a bearing acting vertically downward. .Iaddend. .Iadd.89. Abridge type coordinate measuring machine as described in claim 88,wherein said horizontally acting bearing acts outwardly. .Iaddend.